The manufacture and assembly of structures and structural components has increasingly involved the use of bonded joints or bondlines, such as adhesive bonded joints or bondlines, instead of fastener devices, to bond or join the structural components together. Adhesive bonded joints may be used in bonding of composite structural components in combination with other composites or other materials such as metal. In this regard, adhesive bonded composite structures and structural components may typically be used in the manufacture and assembly of aircraft, spacecraft, rotorcraft, watercraft, automobiles, trucks, buses, and other vehicles and structures due to the design flexibility and low weight of such composite structures and structural components.
Known inspection methods and devices exist for assessing the integrity of adhesive bonded joints or bondlines in order to measure the quality, soundness, effectiveness, performance, strength, or other characteristics of the adhesive bond, as well as to assess the ability of the adhesive bond to function reliably as required throughout the predicted lifetime of the bonded structure or structural components. Such known inspection methods and devices may include a variety of time-consuming techniques such as visual inspection, localized non-destructive inspection methods, laser bond and ultrasonic inspection devices, or other known methods and devices. These known inspection methods and devices may require that the hardware be pulled out of service for the inspection and may not have the ability to interrogate the bondline while the component part is in-service. In addition, such inspection methods and devices may increase costs and flow time to the process of assuring bondline integrity. Moreover, such known inspection methods and devices may only be carried out at certain times or on a periodic basis, rather than having the information about the bondline integrity available at all times on demand and available on a continuous, real time basis.
In particular, known visual inspection and localized non-destructive inspection methods and devices may not be effective where visual access to the adhesive bonded joints or bondlines is limited or not possible, for example, if such adhesive bonded joints or bondlines are located in a remote or interior location or beneath the surface. Access to interior bonded joints and bondlines may be difficult or not possible without disassembly or damage to the structures or structural components, such as removing a part or drilling a hole into a structure for insertion of a measurement tool. In addition, ultrasonic inspections may require specialized equipment, substantial operator training, and effective access to the structural component.
In addition, known methods and devices exist for monitoring the health of a composite structure with the use of external sensors. For example, U.S. Patent Publication Number 2007/0166831 A1 to Watkins, Jr. et al., discloses a method for monitoring the health of a composite structure by disposing a condition sensor on the surface of the composite structure. However, positioning sensors on the external surface of the structure may provide measurements of the whole structure including measurements through the structural components and the bondline. Such known methods and devices may provide only indirect and less accurate measurements of bondline characteristics and not direct and more accurate measurements of bondline characteristics at or within the bondline. In addition, alignment and positioning of external sensors may be complicated by accessibility to the structure or structural component, for example, inaccessibility to one side of a composite sandwich structure.
Accordingly, there is a need in the art for an improved system and method for monitoring bonding integrity directly at or within adhesive bonded joints or bondlines of structures or structural assemblies where such improved system and method provide advantages over known systems and methods.
A related aspect of monitoring the integrity of adhesively-bonded joints is with regard to detecting and monitoring high-intensity transient electrical currents that may pass through bonded joints. For example, aircraft must be capable of withstanding high-intensity current due to lightning strikes. In view of the undesirable effects of high-intensity electrical current on adhesive, and considering the increasing use of adhesively-bonded joints in the primary structure of an aircraft, it is becoming necessary to detect and monitor electrical current flow through bonded joints as may occur in the event of a lightning strike. In this regard, it is necessary to understand the distribution of current flow from a lightning strike toward and through bonded joints to facilitate the testing, design, and development of aircraft structures capable of withstanding or avoiding excessively-high current flow through bonded joints. As indicated above, known methods for assessing the integrity of adhesively-bonded joints are limited to time-consuming techniques such as visual inspection, localized non-destructive inspection methods, the use of laser bond and ultrasonic inspection devices, or other known methods and devices.
Accordingly, there exists a need in the art for a system and method for detecting and monitoring electrical current flow through bonded joints so that appropriate lighting protection may be provided to such bonded joints.